1. Field of the Invention
This invention relates generally to a wire-welding device, and more particularly to an apparatus for stitch welding a continuous insulated wire to a plurality of terminal pins mounted on a circuit board.
2. Description of the Prior Art
It is well known in the art that various problems and difficulties are being encountered in providing suitable means for welding continuous insulated wire to various terminal pins positioned on circuit boards.
There are many well-known methods and types of wirewelding apparatuses presently in use. However, these devices have various individual features that restrict their use; and they are also complicated to operate and expensive to maintain.
Due to the highly advanced technology in the electronics field, the reliability of intricately designed circuit boards has become more critical than heretofore. A circuit board includes large numbers of closely spaced, miniature terminal pins which must be electrically interconnected by welding a continuous insulated wire from one point to another. The welding of the insulated wire is accomplished by forceably pressing the wire, with the electrode, against each terminal pin, so that it ruptures through the insulation to expose the wire for contact with the pin. Welding current is passed through the electrode to weld the central conductor of the wire to the terminal pin. Thus, it is necessary to press the electrode against the wire with great force; and at the same time wire must be accurately positioned on the pin with the wire remaining between the electrode and the terminal pin. It is a time-consuming task to precisely position the wire on the pin.
There is still a further problem that is frequently encountered in that the use of excessive pressure on the wire causes it to be scored to such an extent that a weak link is established in the wire on the weld itself. The weakening of the wire is not often recognizable and eventually this leads to a break, resulting in failure within the electronic system. On the other hand, if the weakened area is noted after the weld has already taken place, the wire must be removed from the pin without further harm to the circuit and the welding operation must be restarted. There are also times when the circuit board becomes so abused that it must be discarded.
The technology of the most commonly employed wirewelding apparatus involves sandwiching the wire and terminal pin between two opposing electrodes, with exactly the proper force required to penetrate the Teflon insulation on both sides (via cold-flowing) and establish positive electrical contact between all elements. This system involves two main mechanical components. The first is a weld-head assembly, designed to raise and lower an upper electrode at required pressures, and to trigger the electrical welding impulse at the proper time. The second is a lower electrode assembly which combines a fixed or pop-up lower electrode with a table-top working surface, in order to balance and manipulate circuit-board workpieces.
Of necessity, these mechanical elements have been packaged in the form of either large refrigerator-sized machines, which utilize computer-programmed X/Y tables, or desk-top-sized, manual, stitch-wiring machines, roughly as large and heavy as a drafting-table top. These manual devices possess inherent disadvantages, among which are the following:
1. Lack of field portability. They cannot be carried by field technicians to work sites for instant on-site repairs or modifications to boards actually installed in working equipment. PA1 2. Locating the board precisely between the opposing electrodes is difficult and time-consuming, requiring both hands. PA1 3. There is insufficient clearance between the open electrodes. Boards must often be unloaded (components and connectors removed) prior to processing. PA1 4. A complex, time-consuming, weld-energy schedule must be run prior to actual operation. PA1 5. Equipment and materials not provided with the basic unit are required in order to perform bonding (i.e., pull test gauges, etc.). PA1 6. Bonding with this device cannot take place on boards such as backplane motherboards which are installed in racks, making manual stitch-wiring machines impractical for them. PA1 U.S. Pat. No. 2,417,819--APPARATUS FOR JOINING WIRES AND THE LIKE BY FUSION, Gilbert Gilliver; PA1 U.S. Pat. No. 3,089,020--INDIRECT WELDING, Richard P. Hurlebaus; PA1 U.S. Pat. No. 3,342,972--WELDING ELECTRODE ASSEMBLY, Mortimer Penberg; PA1 U.S. Pat. No. 3,369,102--EXPOSIVE RIVET DETONATING RIVET TOOL, Theodore M. Jacobs; PA1 U.S. Pat. No. 3,596,044--THROUGH INSULATION WELDING SYSTEM, Leonard Katzin; PA1 U.S. Pat. No. 3,912,900--METHOD FOR FEEDING WIRE FOR WELDING, James C. Arnett; PA1 U.S. Pat. No. 4,110,593--WELDING GUN ADAPTED TO WELD MOVABLE CONTACTS ON WIRE SPRING RELAYS, Crooks et al.; PA1 U.S. Pat. No. 4,171,477--MICRO-SURFACE WELDING, Joseph Funair.
As examples of other types of welding methods and devices, one may refer to the following United States patents: